The hormone erythropoietin (EPO), which interacts with erythropoietin receptor (EPOR), a high affinity cell surface receptor on the developing erythroblasts is critical for normal erythroid development. Intracellular signaling following binding of the ligand to its receptor results in a proliferative response and ensures differentiation of the erythroid lineage. EPO may have other functions too. EPO-R has been detected in placenta and endothelial cells. EPO was also shown to stimulate the production of immunoglobins in B-cells. Recent data in this laboratory indicated that EPOR is expressed in developing brain of the mouse embryo. A 15kb Genomic DNA of the human EPOR has been cloned in this laboratory and two larger human genomic clones containing 85kb fragments were recently isolated. We are using these to study the expression and transcriptional regulation of the EPO-R gene. Preliminary result of in situ hybridization using a RNA probe generated by in vitro transcription of EPOR cDNA to nine day mouse embryo has shown staining in the head and back area and a streak along the center of the body. These structures are yet to be determined. Transient transfection of eukaryotic cell line is also being used to identify upstream cis-regulatory elements and their regulation by transcription factors.